1. Field of the Invention
The invention relates in general terms to organic, electro-optical elements, and to a process for producing them. In particular, the invention relates to a process for producing hermetically encapsulated organic, electro-optical elements, and to a hermetically encapsulated electro-optical element.
2. Description of Related Art
Organic light-emitting diodes (OLEDs) are the subject of intensive development work, since they have a number of advantages over other illumination and display means. For example, OLEDs can be made very thin and even flexible. Moreover, compared to liquid-crystal displays, OLEDs have the benefit of being self-illuminating.
However, the main problem with OLEDs is their service life, which has hitherto been very limited. It has proven almost impossible to extend the operating time of OLEDs to more than 5000 operating hours. Metal cathodes with a low work function are generally used for OLEDs. In this context, inter alia metallic calcium is customary. However, these materials with a low work function are generally highly reactive. Chemical reactions undergone by the metal layer and associated changes in the work function are considered to be one of the main factors limiting the service life.
In particular the reaction with air or with the water which is present as moisture in the air is responsible in this context for the degradation of the metal electrode of an OLED.
To solve the problem, U.S. Pat. No. 5,882,761 proposes an OLED in which the OLED structures are covered with a curved metal sheet. In addition, the OLED described in that document has a reservoir of drying agent or getter. The drying-agent reservoir and the OLED structures are separated from one another by a porous adhesive tape. The metal sheet is joined to the glass substrate by means of a UV adhesive. A drawback of this solution is that organic layers, such as the bonding area between metal sheet and glass substrate, are relatively easy for small gas molecules to penetrate. Therefore, the adhesive bonding represents a passage, in particular for atmospheric oxygen and water. Therefore, it is only a question of time until the drying agent is exhausted and degradation of the metal electrode commences. Furthermore, this type of encapsulation makes it impossible to implement significant properties of the OLED technology, such as the encapsulation of extremely thin or flexible components.
Examples of known getter materials are liquids such as those described in JP 7211456, U.S. Pat. No. 5,821,692, or U.S. Pat. No. 5,962,962. Furthermore, EP 0776147 describes the use of solid-state materials as getters. As disclosed in WO 99/03112, gases can also be used as getter medium for organic components. However, a common feature of all these solutions which are known from the prior art is that the efficiency of the getter material falls as the incidence of gas continues, and consequently there is no permanent protection against degradation.